Wind turbine electromechanical torsional vibration testing device and testing method

Abstract

The present invention relates to a wind turbine electromechanical torsional vibration test device and test method, the device comprises a host computer, a power grid simulator and a coupling transformer connected in sequence, the power grid simulator comprises a control module, a fundamental wave module and a secondary wave module, the control module and the coupling transformer are respectively connected to the fundamental wave module and the secondary wave module, the fundamental wave module is used to simulate the fundamental wave signal of the power grid, the secondary wave module is used to simulate the secondary wave signal of the power grid, the coupling transformer couples the signal generated by the fundamental wave module and the signal generated by the secondary wave module, and the processed signal is transmitted to the wind turbine generator set or the power electronics simulator; the method comprises: obtaining test parameters, the test parameters include test mode, power grid information and generator information, the test mode includes preliminary test mode, direct connection test mode and prediction mode; performing corresponding tests based on the determined test mode. Compared with the prior art, the present invention has the advantages of high reliability of test data and high stability of the test system.

Description

Technical Field

[0001] The invention belongs to the technical field of wind power, relates to an electromechanical torsional vibration testing technology, and in particular to an electromechanical torsional vibration testing device and a testing method for a wind turbine generator. Background Art

[0002] With the continuous increase in installed capacity of wind power generation, due to the particularity of the flexible shaft of the wind turbine, it is easy to experience electromechanical torsional vibration after being connected to the grid, which will cause serious impact on the power grid and wind turbines. Therefore, before the wind turbine is connected to the grid, there is an urgent need for a test method and device that can accurately test the electromechanical torsional vibration of the wind turbine.

[0003] The current test methods for electromechanical torsional vibration are mainly divided into two categories:

[0004] 1) A torsional vibration damping pulley is connected to the driver, and the driver is connected to the motor. Multiple torsional vibration sensors are installed on the motor shaft system. The driver is made to perform variable speed motion under full load conditions. The torsional vibration of the driver itself is used to achieve sweep frequency excitation of the torsional vibration damping pulley, thereby measuring the torsional vibration frequency of the motor. This method of using a torsional vibration damping pulley and a driver to test the torsional vibration frequency of the motor is mostly suitable for low-power applications. Since wind turbines have high voltage and current levels, and large mass and volume, this test method is not suitable for testing wind turbines.

[0005] 2) By installing a data acquisition unit on the shaft system of the nuclear power unit, the current, voltage and other signals of the nuclear power unit are collected and transmitted to the data processing unit for centralized analysis and processing, thereby playing a good role in monitoring the state of the nuclear power unit shaft system. The test method of installing a data acquisition unit on the shaft system of the generator set and transmitting the collected data to the data processing unit for centralized processing has the disadvantages of unreliable collection accuracy, delayed information transmission, and difficulty in giving a torsional vibration judgment standard. It is mostly used for status monitoring after the generator set is connected to the grid, and is not suitable for torsional vibration testing before the generator set is connected to the grid. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a wind turbine electromechanical torsional vibration testing device and testing method with high test data reliability and high test system stability, which can reliably find out the torsional vibration frequency of the wind turbine, correct the damping coefficient, and thus reduce power loss.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A wind turbine electromechanical torsional vibration test device, which is used to connect to a wind turbine generator set or a power electronics simulator, and includes a host computer, a power grid simulator and a coupling transformer connected in sequence. The power grid simulator includes a control module, a fundamental wave module and a secondary wave module. The control module and the coupling transformer are respectively connected to the fundamental wave module and the secondary wave module. The fundamental wave module simulates a power grid fundamental wave signal under the control of the control module, and the secondary wave module simulates a power grid secondary wave signal under the control of the control module. The coupling transformer couples the signal generated by the fundamental wave module and the signal generated by the secondary wave module, and the processed signal is transmitted to the wind turbine generator set or the power electronics simulator.

[0009] Furthermore, the power grid simulator is a five-level power grid simulator.

[0010] Furthermore, the fundamental wave module and the secondary wave module are both improved half-bridge MMC sub-modules, in which the capacitor C 0 The two ends are connected in parallel with a series resistor R 1 And voltage regulator VD 3 .

[0011] Furthermore, the control module includes a main controller, a first slave controller and a second slave controller, the main controller, the first slave controller and the fundamental wave module are connected in sequence, and the main controller, the second slave controller and the secondary wave module are connected in sequence.

[0012] Furthermore, the main controller adopts a DSP controller.

[0013] Furthermore, both the first slave controller and the second slave controller are FPGA controllers.

[0014] Furthermore, the testing device also includes an information interaction module for communicating with the wind turbine generator set.

[0015] The present invention also provides a method for testing the electromechanical torsional vibration of a wind turbine generator using the electromechanical torsional vibration testing device for the wind turbine generator as described above, the method comprising the following steps:

[0016] Acquire test parameters, wherein the test parameters include a test mode, grid information, and generator information, wherein the test mode includes a preliminary test mode, a direct connection test mode, and a prediction mode;

[0017] Execute corresponding tests based on the determined test mode;

[0018] Wherein, in the preliminary test mode, the test device is connected to a power electronic simulator loaded with a wind turbine model, and the secondary wave information coupled in the output of the power grid simulator is continuously adjusted until the wind turbine model in the power electronic simulator shows an electromechanical torsional vibration condition, or the test time reaches a specified test time, the test ends, and the electromechanical torsional vibration information is output;

[0019] In the direct connection test mode, the test device is directly connected to the wind turbine, and based on a given wind turbine damping coefficient, the secondary wave information coupled in the output of the power grid simulator is continuously adjusted until the wind turbine has an electromechanical torsional vibration condition, or the test time reaches a specified test time, the test ends, and the electromechanical torsional vibration information is output;

[0020] In the prediction mode, the test device is connected to a power electronics simulator loaded with a trained wind turbine model, and based on an electromechanical torsional vibration prediction algorithm, combined with real-time information of the power grid and the wind turbine, predicts the conditions for the occurrence of electromechanical torsional vibration in advance, transmits the electromechanical torsional vibration information to the wind turbine generator set, and changes the additional damping coefficient of the wind turbine.

[0021] Furthermore, the fundamental wave module and the secondary wave module are both improved half-bridge MMC sub-modules, in which the capacitor C 0 The two ends are connected in parallel with a series resistor R 1 And voltage regulator VD 3 .

[0022] Furthermore, the improved half-bridge MMC submodule is controlled by a voltage balancing control strategy, and the voltage balancing control strategy specifically includes:

[0023] (1) Setting the capacitor voltage lower limit A, the first capacitor voltage upper limit B, and the second capacitor voltage upper limit C of each MMC submodule, where C is greater than B, and setting the holding factors a and b;

[0024] (2) At time t0, the capacitor voltage and input status of each MMC submodule are collected and transmitted to the control module;

[0025] (3) Determine the direction of the bridge arm current at time t1. If the bridge arm current at time t1 causes the put-in-place MMC submodule to charge, execute step (4); if the bridge arm current at time t1 causes the put-in-place MMC submodule to discharge, execute step (5);

[0026] (4) Determine the number of MMC submodules that need to be put into use at time t1, multiply the capacitor voltage of the submodules that are in the cut-off state and whose capacitor voltage is higher than A by the retention factor a, and then sort them, and put the submodules into use in the order of the submodule capacitor voltage from small to large;

[0027] (5) Determine the direction of the bridge arm current at time t2. If the direction of the bridge arm current at time t2 causes the put-in module to charge, the submodules in the cut-off state and whose capacitor voltage is greater than B and the submodules in the put-in state are multiplied by the retention factor b and then sorted; if the direction of the bridge arm current at time t2 causes the put-in module to discharge, the submodules in the cut-off state and whose capacitor voltage is between B and C and the submodules in the put-in state are multiplied by the retention factor b and then sorted. The submodules with a capacitor voltage greater than C are connected through the resistor R 1 And voltage regulator VD 3 Discharge to below C;

[0028] (6) Determine the number of MMC sub-modules that need to be put into use at time t1, and put the sub-modules into use at time t1 in the order of the sub-module capacitance voltage from large to small;

[0029] (7) Repeat steps (2) to (6) until the test is completed.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The power grid simulator of the present invention includes a fundamental wave module and a secondary wave module, which are respectively used to simulate the fundamental wave state of the power grid and the secondary wave signal existing in the power grid, and the frequency amplitude of the secondary wave signal is adjustable, which can achieve the purpose of simulating the real situation of the low-frequency secondary wave component in the power grid, and the test data has high reliability.

[0032] 2. The present invention uses two five-level power grid simulators in parallel to realize power grid simulation. Starting from the conditions for the generation of electromechanical torsional vibration, the electromechanical torsional vibration frequency can be directly obtained through testing, and the test is convenient.

[0033] 3. The present invention improves the MMC submodule so that the test device can be more suitable for the electromechanical torsional vibration test of the wind turbine.

[0034] 4. The present invention improves the topology of the MMC submodule and designs an adaptive voltage balancing control strategy to achieve better voltage balancing effect and improve the stability of the test system. The improved half-bridge MMC submodule can reduce the impact of the inverter grid-side fault on the inverter to a certain extent due to the self-discharge function, so as to reduce the failure probability of the MMC submodule. The improved topology can achieve the self-voltage reduction effect under high voltage conditions. In terms of the capacitor voltage balancing control of the fundamental wave module of the test device, the improved bubbling algorithm is used to sort the capacitor voltages of the submodules, which significantly improves the sorting efficiency and shortens the sorting time to shorten the system response time. It is particularly suitable for the converter circuit using FPGA as the controller, and can make full use of the computing resources of the controller.

[0035] 5. The present invention adopts the idea of ​​hardware-in-the-loop testing, directly connects the wind turbine to the test device or downloads the wind turbine model to the power electronics simulator and then connects the power electronics simulator to the test device to implement the test, which is convenient and reliable. The present invention can implement multiple test modes. In the prediction mode, after the power grid model and the wind turbine model are fully trained, the electromechanical torsional vibration conditions of the wind turbine can be predicted in combination with the electromechanical torsional vibration prediction strategy. The damping coefficient of the wind turbine is adjusted in time through the interactive module to reduce the probability of electromechanical torsional vibration of the wind turbine, thereby improving the reliability of the operation of the wind turbine.

[0036] 6. Through the present invention, after improving the accuracy of the electromechanical torsional vibration frequency test data of the wind turbine, the damping coefficient of the wind turbine can be accurately adjusted to avoid power loss under rated conditions caused by an excessively large damping coefficient, thereby improving the power generation efficiency of the wind turbine; avoiding the serious impact of electromechanical torsional vibration on the power grid and the wind turbine caused by the low frequency of the power grid caused by an excessively small damping coefficient, thereby improving the operating reliability of the wind turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a principle block diagram of the device of the present invention;

[0038] Figure 2 It is a topological diagram of the fundamental wave module and the secondary wave module of the present invention;

[0039] Figure 3 This is a connection diagram of test mode 1 of the present invention;

[0040] Figure 4 This is a connection diagram of test mode 2 of the present invention;

[0041] Figure 5 This is a connection diagram of test mode 3 of the present invention;

[0042] Figure 6 This is a schematic diagram of a 50 Hz fundamental wave of a power grid simulator of the present invention;

[0043] Figure 7 This is a schematic diagram of the 10 Hz secondary wave of the power grid simulator of the present invention;

[0044] Figure 8 It is a schematic diagram of the grid voltage waveform containing the secondary wave of the present invention;

[0045] Fig. 9 It is the topology diagram of the traditional half-bridge MMC submodule;

[0046] Fig.10 This is the topological diagram of the improved half-bridge MMC submodule of the present invention;

[0047] Fig.11The topology diagram of the multi-level converter based on the improved MMC submodule of the present invention;

[0048] Fig.12 This is a flow chart of the pressure equalization control strategy of the present invention. DETAILED DESCRIPTION

[0049] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0050] like Figure 1-Figure 5 As shown, this embodiment provides an electromechanical torsional vibration test device for a wind turbine generator, which is used to connect to a wind turbine generator set 5 or a power electronic simulator 4, and includes a host computer 1, a power grid simulator 2 and a coupling transformer 3 connected in sequence, the power grid simulator includes a control module, a fundamental wave module 204 and a secondary wave module 205, the control module and the coupling transformer 3 are respectively connected to the fundamental wave module 204 and the secondary wave module 205, the fundamental wave module 204 simulates a 50Hz power grid fundamental wave signal under the control of the control module, the secondary wave module 205 simulates a power grid secondary wave signal under the control of the control module, the coupling transformer 3 couples the signal generated by the fundamental wave module 204 and the signal generated by the secondary wave module 205, and the processed signal is transmitted to the wind turbine generator set 5 or the power electronic simulator 4 for electromechanical torsional vibration testing.

[0051] The power grid simulator is a five-level power grid simulator to accurately simulate the power grid environment. The secondary wave signal of the power grid can be coupled with the fundamental wave signal of the power grid through an ordinary coupling transformer, which is easy to implement. Figure 6 FIG. 4 is a schematic diagram of a 50 Hz fundamental wave simulated in this embodiment. Figure 7 The 10 Hz secondary wave simulated in this embodiment is shown as follows: Figure 8 Shown is a schematic diagram of a grid voltage wave containing a secondary wave after coupling processing according to this embodiment.

[0052] like Figure 2 As shown, the fundamental wave module 204 and the secondary wave module 205 are both improved half-bridge MMC sub-modules, such as Fig.10 As shown, in the improved half-bridge MMC submodule, the capacitor C 0 The two ends are connected in parallel with a series resistor R 1 And voltage regulator VD 3 , used for self-discharge of the capacitor when the capacitor voltage of the MMC submodule is much higher than the reference value, where the resistor R 1 Resistance value and voltage regulator tube VD 3 The voltage regulation value can be freely adjusted according to the actual application situation to achieve scenarios suitable for different voltage levels. The multi-level converter topology based on the improved MMC submodule is as follows: Fig.11 shown.

[0053] In this embodiment, the control module includes a main controller 201, a first slave controller 202 and a second slave controller 203. The main controller 201, the first slave controller 202 and the fundamental wave module 204 are connected in sequence, and the main controller 201, the second slave controller 202 and the secondary wave module 205 are connected in sequence.

[0054] In this embodiment, the above-mentioned control module adopts a master-slave control architecture of DSP+FPGA, and the master controller adopts a DSP controller for synchronous management of the fundamental wave module and the secondary wave module, fault alarm protection, etc. The first slave controller and the second slave controller both adopt FPGA controllers, which are responsible for the rapid calculation of the power grid model and the generation of the inverter drive signal. Among them, the first slave controller is responsible for the rapid calculation of the fundamental wave power grid model and the generation of the fundamental wave module drive signal, the collection of the voltage and current and other signals of the fundamental wave module, and the voltage balancing control of the fundamental wave module. The second slave controller is responsible for the rapid calculation of the low-frequency power grid model and the generation of the secondary wave module drive signal, the collection of the voltage and current and other signals of the secondary wave module, and the voltage balancing control of the secondary wave module.

[0055] In another embodiment, the testing device further includes an information interaction module for communicating with the wind turbine generator set.

[0056] The wind turbine electromechanical torsional vibration testing method using the wind turbine electromechanical torsional vibration testing device as described above includes the following steps: obtaining test parameters from a host computer interface, the test parameters including test mode, grid information and generator information, the test mode including preliminary test mode, direct connection test mode and prediction mode; performing corresponding tests based on the determined test mode.

[0057] The above test method includes three test modes, which are described in detail as follows.

[0058] Mode 1: If Figure 3 The figure shows the connection diagram of the preliminary test mode. The test device is connected to the power electronic simulator 5 loaded with the wind turbine model, and continuously adjusts the secondary wave information coupled in the output of the power grid simulator 2 until the wind turbine model in the power electronic simulator 2 shows electromechanical torsional vibration conditions, or the test time reaches the specified test time. The test ends and outputs relevant information such as the electromechanical torsional vibration frequency.

[0059] This preliminary test mode is used to preliminarily lock the electromechanical torsional vibration frequency of the wind turbine to avoid damage to the wind turbine due to the electromechanical torsional vibration of the actual test without additional damping.

[0060] Mode 2: If Figure 4The figure shows the connection diagram of the direct test mode. The test device is directly connected to the wind turbine. According to the wind turbine damping coefficient given by the preliminary test data obtained in the mode, the secondary wave information coupled in the output of the power grid simulator is continuously adjusted until the wind turbine has electromechanical torsional vibration conditions, or the test time reaches the specified test time. The test ends and the electromechanical torsional vibration frequency and other related information are output.

[0061] This direct connection test mode is used to accurately test the electromechanical torsional vibration of wind turbines before they are connected to the grid, and the test results are closer to actual engineering applications.

[0062] Mode 3: Figure 5 The figure shows the connection diagram of the prediction mode. The test device is connected to a power electronics simulator loaded with a trained wind turbine model. Based on the electromechanical torsional vibration prediction algorithm, the conditions for the occurrence of electromechanical torsional vibration are predicted in advance in combination with the real-time information of the power grid and the wind turbine. The electromechanical torsional vibration information is transmitted to the wind turbine generator set, the additional damping coefficient of the wind turbine is changed, and the occurrence of electromechanical torsional vibration is avoided.

[0063] In order to cooperate with the improved half-bridge MMC submodule, the present invention also proposes a voltage sharing control strategy when the improved half-bridge MMC submodule is applied to a multi-level converter, such as Fig.12 This control strategy is described as follows:

[0064] (1) Setting the capacitor voltage lower limit A, the first capacitor voltage upper limit B, and the second capacitor voltage upper limit C of each MMC submodule, where C is greater than B, and setting the holding factors a and b, where a and b are both slightly greater than 1 and can be set according to actual conditions;

[0065] (2) At time t0, the capacitor voltage and input status of each MMC submodule are collected and transmitted to the control module;

[0066] (3) Determine the direction of the bridge arm current at time t1. If the bridge arm current at time t1 causes the put-in-place MMC submodule to charge, execute step (4); if the bridge arm current at time t1 causes the put-in-place MMC submodule to discharge, execute step (5);

[0067] (4) In this case, the sub-modules with lower capacitor voltages tend to be put into use at time t1. The number of MMC sub-modules that need to be put into use at time t1 is determined. The capacitor voltages of the sub-modules that are in the cut-off state and whose capacitor voltages are higher than A are multiplied by the retention factor a and then sorted. The sub-modules are put into use in the order of the sub-module capacitor voltages from small to large.

[0068] (5) Determine the direction of the bridge arm current at time t2;

[0069] a) If the direction of the bridge arm current at time t2 causes the put-in module to charge, then at time t1, the submodule whose capacitor voltage is greater than the upper limit B of the submodule capacitor voltage tends to be put in, and the submodules in the cut-off state and whose capacitor voltage is greater than B and the submodules in the put-in state are multiplied by the retention factor b and sorted;

[0070] b) If the direction of the bridge arm current at time t2 causes the switched-in module to discharge, then at time t1, the submodule with a higher capacitor voltage but not exceeding the upper limit C of the submodule capacitor voltage will tend to be switched in. The submodules in the cut-off state and with capacitor voltages between B and C and the submodules in the switched-in state will be multiplied by the retention factor b and sorted. The submodules with a capacitor voltage greater than C will be switched in through the resistor R 1 And voltage regulator VD 3 Discharge to below C;

[0071] (6) Determine the number of MMC sub-modules that need to be put into use at time t1, and put the sub-modules into use at time t1 in the order of the sub-module capacitance voltage from large to small;

[0072] (7) Repeat steps (2) to (6) until the test is completed.

[0073] Through Matlab / Simulink simulation test, this solution can be applied to the electromechanical torsional vibration test of wind turbines. In the above voltage-balanced control strategy, the improved bubble sorting method can be used to achieve sorting, which shows a significant improvement in sorting efficiency when the number of levels is large.

[0074] When the voltage of the submodule capacitor is too high (higher than the set upper limit), and the capacitor of the submodule is discharged at time t1, and the capacitor of the submodule is still discharged at time t2, if this submodule is put into use first, it will cause serious distortion of the output voltage, which is undesirable in actual engineering applications. If the voltage-sharing control algorithm of the present invention is adopted, this submodule will not be put into use at this time, but will be put into use after voltage reduction treatment, and it will pass through the resistor R 1 And voltage regulator VD 3 A discharge loop is formed to release the submodule capacitor voltage to a preset reference value, and the submodule re-participates in the sorting at time t2, thereby avoiding the serious distortion of the output voltage waveform and improving the operating stability of the test system.

[0075] The improved half-bridge MMC submodule can reduce the impact of the inverter grid-side fault on the inverter to a certain extent due to its self-discharge function, thereby reducing the failure probability of the MMC submodule.

[0076] When the grid-side voltage suddenly rises, its voltage is shared by the improved half-bridge MMC sub-modules put into use on each bridge arm at the current moment. Due to its high-voltage self-discharge function, the capacitor voltage can be reduced to a certain extent, thereby avoiding the problem of IGBT being broken down by high voltage, reducing the failure probability of the sub-module and improving the operating stability of the test system.

[0077] In order to overcome the difficulty of existing test methods in applying to the scenario of high voltage and high current of wind turbines, the above test device and test method use a five-level power grid simulator, and send out the simulated power grid fundamental wave signal and secondary wave signal separately with the fundamental wave module and the secondary wave module, and couple the power grid fundamental wave signal and the secondary wave signal through a coupling transformer to simulate the actual situation of the power grid. The output end is connected to the generator or the power electronics simulator with the wind turbine downloaded to perform hardware-in-the-loop experiments, so that the test is more in line with the actual project and the test data is more reliable. The control layer combines the resource management advantages of DSP and the fast computing advantages of FPGA, and adopts the master-slave control method to expand the control port, solve the problem of insufficient control ports of the existing controller, and can achieve the synchronous management and control effect of the fundamental wave signal and the secondary wave signal of the five-level power grid simulator.

[0078] The above technology also improves the traditional half-bridge MMC submodule topology by adding capacitor C 0 The resistor R is added at both ends 1 And the voltage regulator VD 3 , used for self-discharge of the capacitor when the capacitor voltage of the MMC submodule is much higher than the reference value, where the resistor R 1 Resistance value and voltage regulator tube VD 3 The voltage stabilization value can be freely adjusted according to the actual application situation to achieve scenarios suitable for different voltage levels. A voltage balancing control strategy is proposed when the improved half-bridge MMC submodule is applied to the multi-level converter. When the capacitor voltage of the half-bridge MMC submodule is too high, it is not directly put into the converter working circuit, but is put into the converter after self-discharge and voltage reduction through the discharge circuit given in the topology of the improved half-bridge MMC submodule, so as to achieve the purpose of balancing the capacitor voltage of the converter half-bridge MMC submodule and stabilizing the converter output.

[0079] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for testing electromechanical torsional vibration of a wind turbine, characterized in that: The method is implemented based on a wind turbine electromechanical torsional vibration test device, the test device is used to connect a wind turbine generator set or a power electronic simulator, and includes a host computer, a power grid simulator and a coupling transformer connected in sequence, the power grid simulator includes a control module, a fundamental wave module and a secondary wave module, the control module and the coupling transformer are respectively connected to the fundamental wave module and the secondary wave module, the fundamental wave module simulates a power grid fundamental wave signal under the control of the control module, the secondary wave module simulates a power grid secondary wave signal under the control of the control module, the coupling transformer couples the signal generated by the fundamental wave module and the signal generated by the secondary wave module, and the processed signal is transmitted to the wind turbine generator set or the power electronic simulator; The test method comprises the following steps: Acquire test parameters, wherein the test parameters include a test mode, grid information, and generator information, wherein the test mode includes a preliminary test mode, a direct connection test mode, and a prediction mode; Execute corresponding tests based on the determined test mode; Wherein, in the preliminary test mode, the test device is connected to a power electronic simulator loaded with a wind turbine model, and the secondary wave information coupled in the output of the power grid simulator is continuously adjusted until the wind turbine model in the power electronic simulator shows an electromechanical torsional vibration condition, or the test time reaches a specified test time, the test ends, and the electromechanical torsional vibration information is output; In the direct connection test mode, the test device is directly connected to the wind turbine, and based on a given wind turbine damping coefficient, the secondary wave information coupled in the output of the power grid simulator is continuously adjusted until the wind turbine has an electromechanical torsional vibration condition, or the test time reaches a specified test time, the test ends, and the electromechanical torsional vibration information is output; In the prediction mode, the test device is connected to a power electronics simulator loaded with a trained wind turbine model, and based on an electromechanical torsional vibration prediction algorithm, combined with real-time information of the power grid and the wind turbine, predicts the conditions for the occurrence of electromechanical torsional vibration in advance, transmits the electromechanical torsional vibration information to the wind turbine generator set, and changes the additional damping coefficient of the wind turbine.

2. The wind turbine electromechanical torsional vibration test method according to claim 1, characterized in that: The power grid simulator is a five-level power grid simulator.

3. The wind turbine electromechanical torsional vibration test method according to claim 1, characterized in that: The fundamental wave module and the secondary wave module are both improved half-bridge MMC sub-modules. In the improved half-bridge MMC sub-module, a resistor R1 and a voltage regulator tube VD3 are connected in series in parallel at both ends of a capacitor C0.

4. The wind turbine electromechanical torsional vibration test method according to claim 1, characterized in that: The control module includes a main controller, a first slave controller and a second slave controller. The main controller, the first slave controller and the fundamental wave module are connected in sequence. The main controller, the second slave controller and the secondary wave module are connected in sequence.

5. The wind turbine electromechanical torsional vibration test method according to claim 4, characterized in that: The main controller adopts a DSP controller.

6. The wind turbine electromechanical torsional vibration test method according to claim 4, characterized in that: The first slave controller and the second slave controller both adopt FPGA controllers.

7. The wind turbine generator electromechanical torsional vibration test method according to claim 1, characterized in that: The testing device also includes an information interaction module for communicating with the wind turbine generator set.

8. The wind turbine electromechanical torsional vibration test method according to claim 1, characterized in that: The fundamental wave module and the secondary wave module are both improved half-bridge MMC sub-modules. In the improved half-bridge MMC sub-module, a resistor R1 and a voltage regulator tube VD3 are connected in series in parallel at both ends of a capacitor C0.

9. The wind turbine electromechanical torsional vibration test method according to claim 8, characterized in that: The improved half-bridge MMC submodule is controlled by a voltage balancing control strategy, wherein the voltage balancing control strategy specifically includes: (1) Setting the capacitor voltage lower limit A, the first capacitor voltage upper limit B, and the second capacitor voltage upper limit C of each MMC submodule, where C is greater than B, and setting the holding factors a and b; (2) At time t0, the capacitor voltage and input status of each MMC submodule are collected and transmitted to the control module; (3) Determine the direction of the bridge arm current at time t1. If the bridge arm current at time t1 causes the put-in-place MMC submodule to charge, execute step (4); if the bridge arm current at time t1 causes the put-in-place MMC submodule to discharge, execute step (5); (4) Determine the number of MMC submodules that need to be put into use at time t1, multiply the capacitor voltage of the submodules that are in the cut-off state and whose capacitor voltage is higher than A by the retention factor a, and then sort them, and put the submodules into use in the order of the submodule capacitor voltage from small to large; (5) Determine the direction of the bridge arm current at time t2. If the direction of the bridge arm current at time t2 causes the put-in module to charge, the submodules in the cut-off state and whose capacitor voltage is greater than B and the submodules in the put-in state are multiplied by the retention factor b and then sorted; if the direction of the bridge arm current at time t2 causes the put-in module to discharge, the submodules in the cut-off state and whose capacitor voltage is between B and C and the submodules in the put-in state are multiplied by the retention factor b and then sorted, and the submodules whose capacitor voltage is greater than C are discharged to below C through the resistor R1 and the voltage regulator VD3; (6) Determine the number of MMC sub-modules that need to be put into use at time t1, and put the sub-modules into use at time t1 in the order of the sub-module capacitance voltage from large to small; (7) Repeat steps (2) to (6) until the test is completed.

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